Diffusiophoretic water filtration device with closed channel structure

ABSTRACT

A diffusiophoretic water filtration device has a pressurizable gas chamber for receiving a pressurized gas; an inlet manifold for receiving a colloidal suspension including colloidal particles in water; a flow chamber having an inlet and an outlet, the flow chamber for receiving the colloidal suspension at the inlet from the inlet manifold, the colloidal suspension flowing between the inlet and at least one outlet in a flow direction; and a gas membrane separating the gas chamber and the flow chamber, the sheet being made of a gas permeable membrane, the pressurized gas capable of permeating the membrane, the membrane being water impermeable, the gas membrane having a first side facing the pressurized gas chamber, and a second side facing the flow chamber, the flow chamber having a plurality of channels, each channel contacting the second side of the membrane; and an outlet splitter separating a first outlet from a second outlet and splitting the plurality of channels, the first outlet for receiving water having a higher concentration of some of the colloidal particles than the second outlet.

This application claims priority to U.S. Provisional Patent Application62/587,510, filed Nov. 17, 2017, the entirety of which is herebyincorporated by reference herein, and is a divisional of U.S. patentapplication Ser. No. 15/861,273, filed Jan. 3, 2018, the entirety ofwhich is also hereby incorporated by reference herein. This applicationrelates generally to water filtration and more particularly to adiffusiophoretic water filtration device.

BACKGROUND

The article “Membraneless water filtration using CO2” by Shin et al.(Nature Communications 8:15181), 2 May 2017, hereby incorporated byreference herein, describes a continuous flow particle filtration devicein which a colloidal suspension flows through a straight channel in agas permeable material made of polydimethylsiloxane (PDMS). A CO2 gaschannel passes parallel to the wall and dissolves into the flow stream.An air channel on the other side of the wall prevents saturation of CO2in the suspension and the resulting gradient of CO2 causes particles toconcentrate on sides of the channel, with negatively charged particlesmoving toward the air channel and positively charged particles towardthe CO2 channel. The water away from the sides of the channel can becollected as filtered water.

The article “Diffusiophoresis at the macroscale” by Mauger et al.(arXiv: 1512.05005v4), 6 Jul. 2016, hereby incorporated by referenceherein, discloses that solute concentration gradients caused by saltssuch as LiCl impact colloidal transport at lengthscales ranging roughlyfrom the centimeter down to the smallest scales resolved by the article.Particles of a diameter of 200 nm were examined.

The article “Origins of concentration gradients for diffusiophoresis” byVelegol et al, (10.1039/c6sm00052e), pages 4686 to 4703, 13 May 2016,hereby incorporated by reference herein, describes diffusiophoresispossibly occurring in georeservoir extractions, physiological systems,drying operations, laboratory and industrial separations,crystallization operations, membrane processes, and many othersituations, often without being recognized.

PCT Publication WO 2015/077674 discloses a process that places amicroparticle including a salt in proximity to a membrane such that themicroparticle creates a gradient generated spontaneous electric field ora gradient generated spontaneous chemiphoretic field in the solventproximal to the membrane. This gradient actively draws chargedparticles, via diffusiophoresis, away from the membrane thereby removingcharged particulate matter away from the membrane or preventing itsdeposition.

SUMMARY OF THE INVENTION

The present invention provides a water filtration device comprising:

a pressurized gas chamber receiving a pressurized gas;

an inlet manifold receiving a colloidal suspension including colloidalparticles in water;

a flow chamber having an inlet and an outlet, the flow chamber receivingthe colloidal suspension at the inlet from the inlet manifold, thecolloidal suspension flowing between the inlet and at least one outletin a flow direction; and

a horizontal sheet separating the gas chamber and the flow chamber, thesheet being made of a gas permeable membrane, the gas capable ofpermeating the membrane, the membrane being water impermeable, the gasbeing carbon dioxide and permeating the membrane upwardly from the gaschamber in a direction normal to the membrane so as to inducediffusiophoretic motion on at least some of the colloidal particlesopposite to or in the direction normal to the membrane, the sheetcovering a top of the pressurized gas chamber;

the flow chamber being a closed flow chamber having an air permeablecover and a channel structure contacting the colloidal suspension, so asto define a thickness between the cover and the horizontal sheet; and

the at least one outlet having a first outlet spaced above a secondoutlet, the first outlet for receiving water having a higherconcentration of some of the colloidal particles than a second outlet.

The present invention advantageously permits the use of a sheet, such asa PDMS sheet, rather than the complicated channel structure of the priorart. The channel structure, whether provided in one piece with the coveror as a separate structure as described below, can be easilymanufactured, and easily placed on the sheet to create a flow chamber.The channel structure also can be removable to provide for easycleaning, for example by pressurized water.

One preferred PDMS sheet is a PDMS silicone membrane available fromSpecialty Silicone Products, Inc. of Ballston Spa, N.Y.

A preferred thickness of the sheet may be from 10 micrometers to 250micrometers, and most preferably from 20 micrometers to 100 micrometers.

The sheet preferably is at least 5 cm wide by 5 cm long, although largerwidths and lengths are preferred, preferably at least 1 m wide by 1 mlong.

The sheet preferably is unstructured, although open structuring such asribbing or channels in the length direction is possible.

The sheet preferably has a Shore A of between 40 and 60, and a tensileelongation of at least 1000 psi. The elongation to failure is preferablyat least 200%, and most preferably at least 400%, and the tear B is atleast 150 ppi.

All of the sheet values, including thickness, are advantageous formanufacture of the present device, as the sheet can be stretched tautfor example to provide an excellent flow surface while still providingexcellent gas permeability.

Flow velocity through the closed flow chamber can be controlledaccurately via the input pressure, for example via a water pressurereducing valve or a water pressure regulator. An inlet manifold thus canprovide the colloidal suspension at a defined and variable pressure tothe inlet of the flow chamber, and thus also can contain a waterpressure regulator. The pressure for example can be set at a definedpressure, for example via height regulation or a pump. Inlet manifold asdefined herein is thus any structure that provides a predefined widthfor the colloidal suspension to the inlet of the flow chamber.

In one embodiment, the cover may be made in one piece together with achannel structure of longitudinally extending microchannels, each forexample of a thickness of 500 micrometers, width of 900 micrometers andextending a meter in length. The cover and channel structure thus may beetched for example via soft lithography into a single piece of PDMSmaterial. A PDMS barrier between the channels in the width direction of100 micrometers can be provided, so that for a width of 1 m, 1000microchannels can be provided, if for example the two edge barriers are50 micrometers wide. The single piece 1 m×1 m cover and channelstructure can be laid over the PDMS sheet, which due to the airpressure, presses against the cover from below and forms stablemicrochannels. This embodiment provides microchannels for excellentfluid velocity control, and is easily detachable and cleanable. Thecover for example can be removed and the channels and the PDMS sheetsprayed with high velocity water. The device can then be quicklyreassembled. The distance between an outer surface of the cover facingair, and the top of the channel structure can be for example 10 to 25micrometers.

In a second alternate embodiment, the channel structure is providedseparately from the cover, and is sandwiched by the sheet and the cover.In this embodiment, the cover may be similar to the sheet describedabove, and the channel structure may be for example a rectangle made ofPVC or other plastic material with longitudinally extending channelsopen on the top and bottom to define longitudinally extending holes. Thechannel structure thus may be for example 500 micrometers thick, and theholes 900 micrometers wide and extending a meter in length. At the frontend the structure can be connected so that the inlet is provided byplacing a colloidal suspension supply over the holes, and the rear endcan have an outlet structure to divide the outlet stream by connectingthe holes at a certain height, for example extending in a V-shape to arear thickness of 25 micrometers between 125 and 150 micrometers.

The separate channel structure also can be removed from the bottom sheetand the cover and cleaned easily.

In both the first and second embodiments, longitudinally extendingclamps can be provided at both sides so that the cover and channelstructure are clamped with respect to the sheet. A flange on the gaschamber can be used as a counter surface for the clamp, and the clampscan also provide the tautness for the sheet, or this can be providedseparately, for example by a reel mechanism.

In both the first and second embodiments, alternate channel structurescan be provided, for example depending on the type of colloidalsuspension being filtered. Thinner channels structures down to forexample 20 micrometer thickness or less could be provided if thecolloidal particles and other particles to be removed were sufficientlysmall. Also wider channels of 10000 micrometers (1 cm) or larger arepossible, which can make fouling with non-colloidal particles lesslikely.

The structure of both the first and second embodiments allows for easyswapping of various channel structures, by providing in the firstembodiment a different one piece cover and channel structure, and in thesecond embodiment by providing a different channel structure.

The pressurized gas preferably can be carbon dioxide, preferablypressurized to at least 120 kPa and most preferably to at least 130 kPa,preferably between 130 kPa and 200 kPa. As the channel thicknessincreases higher pressures may be desirable to create stronger pressuregradients.

The at least one outlet advantageously can include a movable splitterfor altering the size of the first outlet. For example, the first outletmay be located next to the sheet, and the splitter may be spaced fromthe sheet, and movable to alter a distance between the splitter and thesheet, so that a size of the first outlet is altered. Preferably, as thefirst outlet increases in size the second outlet decreases in size andvice versa.

The first outlet size may be altered as a function of the particles inthe water exiting through the at least one outlet, for example anefficiency of the filtration. For example, if the amount of certaincolloidal particles in the water in the second outlet exceeds a certainthreshold, the first outlet size can be increased.

Another advantage of the present invention is that while the colloidalparticles are in suspension and will not move downwardly on their owndue to gravity, it is supposed that as the colloidal particlescongregate and move downwardly due to diffusiophoresis, they may beaided by gravity. The horizontal configuration also has advantages insimplified outlet construction, as water can be removed easily throughthe first outlet with the aid of gravity. In addition, sincenon-colloidal larger particles can also be filtered, the gravity can aidin the movement of these particles. Thus, the filter of the presentinvention can be used as a sedimentation aid for non-colloidal particlesas well.

While the present application claims a specific structure, otherinventive concepts that may be broader than the present claims, such asa diffusiophoretic water filtration device with a flow chamber separableinto at least parts, to provide for easy cleaning, a diffusiophoreticwater filtration device with a clamped flow chamber, and adiffusiophoretic water filtration device with a variable outlet, adiffusiophoretic water filtration device for filtering noncolloidalparticles of larger sizes as well as methods for constructing, operatingand cleaning a diffusiophoretic water filtration device, are containedherein, and may be claimed in further continuing applications. Moreover,several features claimed, including the horizontal orientation of thedevice, type of gas, and thickness of the flow chamber, areadvantageous, but may not be necessary to a broader inventive conceptthat may be claimed in further continuing applications.

The present invention thus provides for example a diffusiophoretic waterfiltration device comprising: a pressurizable gas chamber for receivinga pressurized gas; an inlet manifold for receiving a colloidalsuspension including colloidal particles in water; a flow chamber havingan inlet and an outlet, the flow chamber for receiving the colloidalsuspension at the inlet from the inlet manifold, the colloidalsuspension flowing between the inlet and at least one outlet in a flowdirection; a gas membrane separating the gas chamber and the flowchamber, the sheet being made of a gas permeable membrane, thepressurized gas capable of permeating the membrane, the membrane beingwater impermeable, the gas membrane having a first side facing thepressurized gas chamber, and a second side facing the flow chamber, theflow chamber having a plurality of channels, each channel contacting thesecond side of the membrane; and an outlet splitter separating a firstoutlet from a second outlet and splitting the plurality of channels, thefirst outlet for receiving water having a higher concentration of someof the colloidal particles than the second outlet.

The present invention thus also provides a diffusiophoretic waterfiltration device comprising: a gas chamber; a flow chamber having aninlet and an outlet; and a gas permeable membrane separating the gaschamber and the flow chamber, the membrane having a first side and asecond side, the first side contacting the gas chamber and the flowchamber having a plurality of channels, each channel of the plurality ofchannels contacting the second side of the membrane.

The present invention thus also provides a diffusiophoretic waterfiltration device comprising: a gas chamber; a flow chamber having aninlet and an outlet; a gas permeable membrane separating the gas chamberand the flow chamber, the membrane having a first side and a secondside, the first side contacting the gas chamber and the second sidecontacting the flow chamber; the flow chamber having at least twoside-by-side channels; and an outlet splitter spaced evenly from themembrane and dividing the at least two side-by-side channels.

BRIEF DESCRIPTION OF THE DRAWINGS

One schematic embodiment of the water filtration system of the presentinvention is shown by reference to:

FIG. 1, which shows a schematic view of the system;

FIG. 2, which shows an embodiment of the water filtration device of thepresent invention schematically;

FIG. 3 shows a schematic top view of the water filtration device of FIG.2;

FIG. 4 shows a schematic cross sectional view a first embodiment of aflow chamber including a sheet and one piece cover and channelstructure;

FIG. 5 shows a schematic cross sectional view of a second embodimentwith a flow chamber including two sheets and a sandwiched channelstructure;

FIG. 6 shows an inlet area of the flow chamber of FIG. 5 schematically;

FIG. 7 shows an outlet area of the flow chamber of FIG. 5 schematically;and

FIG. 8 shows a variable outlet splitter.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 shows a water filtration system 100 for cleaning river water,which may contain various particles such as colloidal plastic ormetallic particles, and other bioparticles such as bacteria and viruses.Many of these particles are charged negatively or positively. Any typeof water with charged colloidal particles may be filtered using thepresent invention. “Colloidal particle” as defined herein is anyparticle that can form a colloid or colloidal suspension in water. Suchcolloidal particles typically range in sizes of a micrometer or less,but larger sizes are possible. The present invention is not limited tofiltering colloidal particles, but can also be used to filter largerparticles that are impacted by diffusiophoresis, for example even up to100 nanometers in size or larger, from water. Preferably the particlesto be filtered are less than 250 nanometers in size, even if notcolloidal. These non-colloidal particles can have very low sedimentationrates, and thus the present invention can aid in “sedimentation” orforcing these larger particles downwardly.

Water filtration system 100 includes a pump 110 pumping water from ariver. The pump 110 pumps the water through a sand filter 120 to removelarger particles and impurities. The water with suspended colloidalparticles, i.e. a colloidal suspension, then passes to the waterfiltration device 200 of the present invention.

Water filtration device 200 is designed to remove positively chargedcolloid particles and other particles, the removal of which cansignificantly increase the water quality.

Water filtration device 200, shown in FIG. 2 schematically, has an inletmanifold 210 receiving pond water with colloidal particles, preferablyhaving passed through a preliminary filter or sedimentation device, suchas sand filter 120. However, water filtration device 200 could beupstream of sand filter 120, thereby removing bacteria and otherparticles that can foul the sand filter 120. Separate water filtrationdevices 200 could also be both upstream and downstream of sand filter120.

Inlet manifold 210 spreads the water with colloidal particles in thewidthwise direction (into the page in FIG. 2) from a pipe received fromsand filter 120. In this example the water with colloidal particles isspread in the inlet manifold to a width of 1 m, and is maintained at adepth d of 1 cm, which height thus regulates the pressure of thesuspension that flows into a flow chamber 212. Larger heights canprovide larger pressures, and thus faster velocities through the flowchamber 212. The height or a pump can also be used to set the inputpressure to a setpoint, for example 1 mbar.

A pressurized gas chamber 220 receives a pressurized gas, such as carbondioxide, from for example pressurized canisters or an industrial source.Gas chamber 220 has gas tight walls 226, over which sheet 222 can bestretched taut and fastened to in a gas tight manner, for example withfasteners and a sealant. The pressurized gas thus can exit in a uniformmanner through the sheet 222. Sheet 222 thus defines the top of gaschamber 220 and the bottom of flow chamber 212.

The colloidal suspension flows from inlet manifold 210 to flow chamber212 via an exit. Flow chamber 212 can have water tight sidewallsextending from and sealed with respect to sheet 222, and may have amicrofluidic or fluid structure therein as will be described. Thecolloidal suspension thus flows between inlet manifold 210 and twooutlets 230, 240 in a flow direction, and, with the closed flow chamber212 of the present invention, the sheet 222 preferably is in ahorizontal orientation to gain the benefit of any gravitational effectson the colloidal particles as they congregate. Other particles presentin the water, for example up to 100 nanometers or larger in the largestdimension, can also be impacted positively by gravitational effects.

However, other orientations, even vertical, are possible especially formicrofluidic chamber structures where the input pressure is the primaryvelocity driver.

The carbon dioxide gas permeates the sheet or membrane 222 in adirection normal to the sheet or membrane 222, the normal directionbeing vertical in the embodiment shown, so as to induce diffusiophoreticmotion on positively charged colloidal particles opposite to thedirection normal to the membrane, here toward the sheet 222. Negativelycharged colloidal particles can move away from the sheet 222, andpossibly be filtered, split or suctioned from the top of the suspension.The removal of negatively charged colloidal particles is optional andnot necessary in this embodiment.

Outlet 240 thus has water having a higher concentration of positivelycharged colloidal and other particles, defined as waste water althoughit can be re-used or refiltered, than a second outlet 230, which can bedefined as having filtered water.

A splitter 250, extending widthwise in a wing-shaped manner with atrailing edge of the wing facing the stream, is moveable upwardly ordownwardly in this embodiment, and can alter the dimensions of theoutlet 240, and thus outlet 230. This adjustment can be a function ofthe water quality of the filtered water for example, and provides highlyadvantageous control of water quality, for example as the sources to befiltered are impacted, for example by rainwater.

The splitter 250 may be keyed for example for rotation about a shaft 401(FIG. 3), the shaft at one end having a worm gear 402 (FIG. 3) movablefor example by a worm driven by a motor and controller. Very finedistance gradations thus can be achieved. In the example show, splitter250 first can be located at 150 micrometers above the sheet 222 and abottom of the outlet 240, so that for example 350 micrometers of a 500micrometer thick stream passes above the splitter. The distance then canbe adjusted as a function of the colloidal particle distribution in thethickness direction in the stream, and the front edge of the splittercan rotate so that the distance for example can move from about 100micrometers above the sheet 222 to about 200 micrometers, for example.Splitting of between 20 percent and 40 percent of a 500 micrometer thickstream thus is possible.

FIG. 3 shows a schematic top view of the water filtration device of FIG.2, showing channels 300, 301, which extend a length 1 in the flowdirection F, and a width w in a crosswise direction and have a thicknesst (FIG. 2). The exit of inlet manifold 210 extends past front walls 309of the channels, so the input pressure extant in inlet manifold 210 istransferred to the channels 300, 301. As the depth of the water istypically much larger than the thickness t of the channels 300, 301, thepressure in channels 300, 301 can generally be estimated as the pressureat the exit of the inlet manifold 210.

FIG. 4 shows a schematic cross sectional view a first embodiment of aflow chamber 212 including a sheet 222 and one piece cover and channelstructure 310, having channels 300, 301 therein. Each channel 300, 301can for example be of a thickness of 500 micrometers, width of 900micrometers and extending approximately a meter in length. The cover andchannel structure 310 thus may be etched for example via softlithography into a single piece of PDMS material for example. Thestraight channels however also permit mechanical or laser cutting. APDMS barrier b between the channels in the width direction of 100micrometers can be provided, so that for a width of 1 m, 1000microchannels can be provided, if for example the two edge barriers are50 micrometers wide. The single piece 1 m×1 m cover and channelstructure can be laid over the PDMS sheet 222, which due to the airpressure from gas chamber 220, presses against the cover from below andforms stable microchannels. The gas chamber can be formed for example ofmetal, and may have longitudinally extending flanges 221 on both lateralsides. Longitudinally extending clamps 400, 402 thus can contact the topof the one piece cover and channel structure 310 and the bottom of theflange 221. Clamps 400, 402 could be for example a two part structuretightenable for example with bolts or screws or made of an elasticmaterial that springs back to provide the clamping action.

The FIG. 4 embodiment provides microchannels for excellent fluidvelocity control, and is easily detachable and cleanable. The cover forexample can be removed and the channels and the PDMS sheet sprayed withhigh velocity water. The device can then be quickly reassembled. Adistance 311 between an outer surface of the cover facing air, and thetop of the channel structure can be for example 10 to 25 micrometers.

FIG. 5 shows a schematic cross sectional view of a second embodimentwith a flow chamber including sheet 222, a cover 330 formed as a secondsheet and a sandwiched channel structure 320 forming channels 302, 303.In the second alternate embodiment, the channel structure 320 isprovided separately from cover 330, and is sandwiched by the sheet 222and the cover 330. In this embodiment, cover 300 may be similar to sheet222 described above, and channel structure 320 may be for example arectangle made of PVC or other plastic material, or PDMS or otherpolymer material, with longitudinally extending channels open on the topand bottom to define longitudinally extending holes. Channel structure320 thus has a thickness t for example of 500 micrometers, and the holesformed by channels 302, 303 can be 900 micrometers wide and extendingapproximately a meter in length. At the front end, channel structure 320can be connected so that the inlet is provided by placing a colloidalsuspension supply over the holes formed by channels 302, 303, and therear end can have an outlet structure to divide the outlet stream byconnecting the holes at a certain height, for example extending in aV-shape to a rear thickness of 25 micrometers between 125 and 150micrometers.

FIG. 6 shows an inlet area of the flow chamber of FIG. 5 schematically,with the front end of the channel structure 320 shown, and displayinghow cover 330 is offset slightly to the rear with respect to sheet 222to form the inlet distance iw for the channel structure 320. The inletdistance iw preferably is at least as large as thickness t to reducefouling.

FIG. 7 shows an outlet area of the flow chamber of FIG. 5 schematically,with for example the rear of the channels 302, 303 (FIG. 6) of channelstructure 320 being connected by a fixed splitter, for example at aheight of 150 micrometers. The outlet area can be manufactured forexample by micromachining or lasering the PVC material.

FIG. 8 shows a variable outlet splitter 250 rotatable around a shaft401, with the rear end of channels 304 (similar to 302, 303 in FIG. 6)connected at top connector to keep the channels 304 properly spaced.

The second embodiment also may be clamped in a similar manner to thefirst embodiment so that the cover 330, channel structure 320 and sheet222 are clamped to form flow chamber 212. All of the parts can be easilydisassembled and cleaned, for example with clean water sprayed at highpressure.

In the two embodiments shown, on one example, the thickness of thechannels is 500 micrometers, the width 900 micrometers and the length1000 mm. Sheet 222 is approximately 1 m×1 m. An input pressure can befor example 1 mbar, or about 1 cm of input depth. Each channel canproduce a flow velocity of about 0.00132457 m/s and a flow rate of0.0357633 mL/min, and has laminar flow with a Reynolds number of about0.85. The dwell time of the colloidal suspension in the flow chamber 212is approximately 755 seconds. The colloidal particle diffusiophoreticvelocity will vary with colloidal particle zeta potential andconcentration gradients over the thickness of the flow chamber, and theexact velocity for each colloid will vary. However, colloidal particlediffusiophoretic velocities of between 1 to 10 micrometer per second aretypical, as stated in the “Origins of concentration gradients fordiffusiophoresis” noted above at page 4687. Thus most positively chargedcolloidal particles, even if at the top of the input stream at thebeginning of flow chamber 212, will move, by the time the fluid hasmoved through the flow chamber 212 to outlet 240. A diffusiophoreticvelocity of 1 micrometer per second would move colloidal particles by755 micrometers, which is larger than the thickness of the fluid, andthus congregate the positively charged colloidal particles at the bottomof the stream at the outlet 240.

The flow rate overall for 1000 microchannels thus is 35.76 mL/min or2.146 liters per hour, and with a slitter height of 150 micrometers, afiltered water to waste water split ratio is 70% to 30%, and a filteredwater output is 1.5 liters per hour.

The embodiment channel structure described above has a minimum distanceof 500 micrometers, which for most colloidal suspensions is sufficientto reduce fouling. Smaller channel thicknesses of 20 micrometers or evensmaller could be possible depending on the application, but thicknessesof 100 micrometers or more are preferred. The concentration gradientsand diffusiophoretic velocities at higher thicknesses may be smaller,but the laminar flow and length of the flow chamber can compensate forthese effects. A thickness of 600 micrometers for example instead of 500micrometers, with other sizes remaining the same, increases the flowrate to almost 3.91/h, with 2.7 liters per hour of filtered water,almost doubling output. The dwell time is 555 seconds, also leading tomost positively charged colloidal particles moving via diffusiophoresisto congregate at the bottom of the stream by the time they reach outlet240.

To maintain concentration gradients and laminar flow however, channelthicknesses of 1mm or less are preferred, and sufficient to reduce mostfouling.

The present device allows for a simply-constructed, relatively largeflow rate water filtration device that can be generally free of foulingand easy to clean and maintain, all with a low energy consumption.Particles that become lodged in the channel structure can be removedduring cleaning, and blockages are reduced. Thus even smaller channelstructures, such as 20 micrometer thickness channel structures orsmaller could be used, depending on the colloidal particles to befiltered.

The present invention also provides that the partially filteredcolloidal suspension, without the positively charged colloidalparticles, can pass to a negative charged colloid filter in which air ispresent at the bottom and carbon dioxide at the top. In this case thesheet and pressurized gas chamber can be on the top, and move thenegatively charged colloidal particles downwardly throughdiffusiophoretic motion. This optional downstream filter can be usedwith or without first attempting removal of the negatively chargedcolloidal particles from the positively charged colloidal particlefilter described in detail herein, and can be added depending on thetype of colloidal suspension being filtered.

What is claimed is:
 1. A diffusiophoretic water filtration devicecomprising: a pressurizable gas chamber for receiving a pressurized gas;an inlet manifold for receiving a colloidal suspension includingcolloidal particles in water; a flow chamber having an inlet and anoutlet, the flow chamber for receiving the colloidal suspension at theinlet from the inlet manifold, the colloidal suspension flowing betweenthe inlet and at least one outlet in a flow direction; a gas membraneseparating the gas chamber and the flow chamber, the sheet being made ofa gas permeable membrane, the pressurized gas capable of permeating themembrane, the membrane being water impermeable, the gas membrane havinga first side facing the pressurized gas chamber, and a second sidefacing the flow chamber, the flow chamber having a plurality ofchannels, each channel contacting the second side of the membrane; andan outlet splitter separating a first outlet from a second outlet andsplitting the plurality of channels, the first outlet for receivingwater having a higher concentration of some of the colloidal particlesthan the second outlet.
 2. The diffusiophoretic water filtration devicesheet as recited in claim 1 wherein the membrane is a PDMS sheet.
 3. Thediffusiophoretic water filtration device sheet as recited in claim 2wherein the thickness of the sheet is from 10 micrometers to 25micrometers.
 4. The diffusiophoretic water filtration device sheet asrecited in 2 wherein the sheet is at least 5 cm wide by 5 cm long. 5.The diffusiophoretic water filtration device sheet as recited in claim 2wherein the sheet preferably has a Shore A of between 40 and 60, and atensile elongation of at least 1000 psi.
 6. The diffusiophoretic waterfiltration device sheet as recited in 1 wherein the inlet manifolddefines a water pressure regulator.
 7. The diffusiophoretic waterfiltration device sheet as recited in claim 1 wherein the chamber has aremovable cover.
 8. The diffusiophoretic water filter as recited inclaim 7 wherein the cover is made in one piece of PDMS together with achannel structure of longitudinally extending microchannels defining theplurality of channels, each microchannel having a thickness equal to orless than 1 mm.
 9. The diffusiophoretic water filtration device sheet asrecited in claim 7 wherein the channel structure is provided separatelyfrom the cover, and is sandwiched by the sheet and the cover.
 10. Thediffusiophoretic water filtration device sheet as recited in claim 9wherein the cover is made of PDMS and the channel structure of aplastic.
 11. The diffusiophoretic water filtration device sheet asrecited in claim 1 further comprising longitudinally extending clampsclamping the cover and channel structure with respect to the sheet. 12.The diffusiophoretic water filtration device sheet as recited in claim10 wherein the clamp contacts a flange on the gas chamber.
 13. Adiffusiophoretic water filtration device comprising: a gas chamber; aflow chamber having an inlet and an outlet; and a gas permeable membraneseparating the gas chamber and the flow chamber, the membrane having afirst side and a second side, the first side contacting the gas chamberand the flow chamber having a plurality of channels, each channel of theplurality of channels contacting the second side of the membrane. 14.The diffusiophoretic water filtration device as recited in claim 13further comprising an outlet splitter spaced evenly from the membraneand dividing each of the plurality of channels.
 15. Thediffusionphoretic water filtration device as recited in claim 13 whereinthe channels are side-by-side channels.
 16. A diffusiophoretic waterfiltration device comprising: a gas chamber; a flow chamber having aninlet and an outlet; a gas permeable membrane separating the gas chamberand the flow chamber, the membrane having a first side and a secondside, the first side contacting the gas chamber and the second sidecontacting the flow chamber; the flow chamber having at least twoside-by-side channels; and an outlet splitter spaced evenly from themembrane and dividing the at least two side-by-side channels.